1. Field of the Invention
The invention relates to mining and metallurgy, and more particularly, to an apparatus for crushing agglomerated mass.
The invention can effectively be used for crushing hot agglomerated mass and stabilizing sinter lumps in terms of shape and mechanical strength.
The invention can also be employed for crushing large coal lumps, slag skulls (particularly when hot), flagstone blocks, frozen materials and the like.
The terminology used in the description is as follows.
Agglomerated mass is used to denote a sintered agglomeration burden comprising iron ore concentrate, sintered iron ore, limestone, solid fuel (such as coke fines, coal and the like) and other components. As the fuel burns, said components melt, then solidify turning into a strong agglomerated mass.
By sintered cake (agglomerated mass slab) we mean an agglomerated mass of a given geometric shape, as, for example, a rectangular slab.
Sinter is understood to be an agglomerated mass slab crushed to lumps of a specified size.
Standard sinter is understood to be a lump iron ore material obtained by crushing agglomerated mass and suitable, after fines (0 to 5 mm) are screened for blast-furnace smelting.
2. Description of the Prior Art
The performance of blast furnaces in terms of efficiency and specific coke consumption can be improved, all other conditions being equal, by providing an optimum size composition of burden materials, in particular, of sinter.
It is essential that a standard sinter charged into a blast furnace should be free from fines, i.e., particles less than 5 mm across, a preferable size of lumps for blast furnace smelting ranging from 5 to 40 mm, the optimum value being 10 to 20 mm across.
At present, most blast furnaces operate on lumps of iron ore materials measuring 100 mm on the high end of the size range and containing more than 10% of fines up to 5 mm in the standard product (sinter). A large proportion of fines results from the crushing of sinter when charged into skips, this amount being further increased through self-crushing and self-abrasion of lumps of sinter generally larger than 80 mm across as they descend in the blast furnace.
Existing methods and apparatus for obtaining sinter lumps of, for example, 50 mm on the high end of the size range generally embody two- or three-stage crushing and screening with a standard sinter yield of about 50%, fines up to 10 mm being removed by means of screens of various designs.
The main method for crushing an agglomerated mass slab is squeezing (pressing), the breaking action being obtained through a linear static compression of the sintered cake on its hot and cold sites simultaneously or through shear (cutting) or splitting of its individual sections effected with the aid of differently oriented shearing (splitting) forces applied to both cold and hot sides.
Crushing of the agglomerated mass according to the first method is performed with the aid of a jaw and two-roll crushers, and according to the second method, by means of toothed single-shaft crushers.
There is known a method for crushing agglomerated masses consisting in shearing (splitting) and squeezing (pressing) hot agglomerated mass slabs fed from charging devices into work zones of a crushing apparatus with the subsequent application of a constant force from a dynamically mobile system, acting substantially upon the cold side of the sintered cake, and of oppositely oriented static reaction forces, acting substantially upon the hot side of the cake, this resulting in crushing of the sintered cake.
The disadvantages of the above and other known methods of hot agglomerated mass crushing are a very slow build-up of dynamic forces in the process of crushing, prolonged contact of a sintered cake being crushed with work members of the crushing apparatus, absence of selectivity of crushing of agglomerated mass and no regulation whatsoever of the high end of the size range of sinter resulting from crushing of agglomerated mass.
There is known an apparatus for crushing agglomerated mass whose housing accommodates a rotor formed with toothed sprockets set rigidly on a shaft and having a feed and discharging devices.
The apparatus is provided with a bed carrying a bar screen.
A front wall of the apparatus housing accommodates a metal plate protecting it against abrasion.
The feed device is mounted in the top part of the bed and is intended to lift the sintered cake off the sintering pallets of a sintering machine and to feed it into the work zone of the apparatus.
The apparatus operates in the manner set forth below.
A hot sintered cake in the form of an agglomerated mass slab is lifted off a pallet to enter the space between the rotor and the bar screen, resting usually by its hot side upon the bars. The rotor, which revolves at a speed of 6 rpm, rolls by its toothed sprockets over the agglomerated mass slab, generally on the cold side, pushes the agglomerated mass between the bars, while squeezing the cold solidified part of the cake into the hot, still plastic, part thereof. The size of lumps pushed through the bars presents a great variety of length, width and thickness dimensions, as it is possible for a lump equal in thickness to a screen slot width and having much greater length and width dimensions to pass through the screen slots, this making the length and the width of the lumps uncontrollable. In addition, the pushing of the agglomerated mass slab through the screen gives rise to considerable friction forces between the agglomerated mass, the sprocket teeth and the screen bars, and results in an intensive wear of the grates.
The main disadvantages of said apparatus for crushing agglomerated mass are as follows:
operation of the grate and of the rotor under constantly severe thermal and physical conditions at temperatures of up to 900.degree. C. of the hot agglomerated mass;
high abrasive properties of the cold agglomerated mass, which intensify the wear of any working members of the crusher; also there is a high degree of risk for the apparatus as a whole and for its separate elements to be damaged by any off-size stray metallic objects;
a low efficiency of the apparatus, as the sintered cake is broken up by the action of crushing (compressive) and shearing forces, this resulting in a low rate of crushing of the material by the sprocket teeth and the grates, since the rotor speed is low (not more than 6 rpm);
no selectivity in crushing of the sintered cake, as the operation is carried out through crushing of the sintered cake along a predetermined direction, this making it impossible to obtain a standard product with required (controllable) top dimensional limit of lumps by a single-stage crushing process, whereas the system formed with the screen bars and the rotating rotor sprocket is not designed to crush the agglomerated mass slab in three dimensions;
lack of intensive or even a partial extraction of heat from the sinter surface, as the hot agglomerated mass is not crushed to 30-40 mm, whereas the slow speed of the rotor (not more than 6 rpm) is inadequate to ensure a convective heat extraction and removal of heat from the hot sinter lumps. This, in turn, fails to provide a normal operation of sinter coolers, since the sinter lumps charged on the work surface of the coolers are far too large and have a very high internal temperature;
lack of means for enhancing the effectiveness of the screens, as it proves impossible to redistribute the crushed product over the work surface of the screens according to size classes; and
lack of the stability of sinter lumps with regard to shape and mechanical strength, as the apparatus is not rated to provide adequate mechanical action upon the crushed product.